Conventionally, methods for providing a surface of a rubber product with non-adhesive property, sliding property, and other barriering properties such as an anti-blooming property include ones: (1) for addition reacting halogen such as chlorine; (2) for attaching powders such as silica, talc, and corn starch; (3) based on a surface coating such as silicone, fluoroplastics, urethane resin, hydrogel polymer; (4) based on surface modification such as by particular organic acid, inorganic acid, plasma etching, corona discharge treatment; (5) based on surface purification by a solvent treatment; and (6) based on surface extraction by warm water, minute alkali, and acid solution.
Although the method (1) is effective for providing the non-adhesive property and sliding property, there are left such problems of: the deteriorated working environment due to the toxic gas; waste water treatment; and separation of halogen from completed products.
Although the method (2) is frequently adopted as the most general method, there has been pointed out a pollution problem due to powder dust such as during an operation process or upon usage, and particularly, the pollution due to the powders cause various infectious diseases in a medical field, while leaving in fields of precision machine and electronic components such a problem that the powders lead to defective products thereby causing defective adhesion in an adhesion process, for example.
The method (3) is to exemplarily coat a different type of polymer onto a surface of a rubber body via complicated processes, thereby leaving a problem that the nature and physical properties inherent in the rubber is affected or the coating is likely to be dropped out.
The method (4) has a problem of a large-sized processing facility and a complicated treatment process, while the methods (5) and (6) noway allow to expect a sufficient effect in view of the purpose of provision of non-adhesive property and sliding property. Further, there is also left a problem that the composite surface such as by using halogen or with a different type of polymer leads to an increased total cost, because of the recent necessity of separation or classification accompanying to waste of materials and to incineration disposal.
Thus, the present applicant has developed a rubber product surface treating method by virtue of formic acid or acetic acid and hydrogen peroxide (Japanese Patent No. 3,049,230), as a method for solving the problems due to the above-mentioned methods (1) through (6).
According to the rubber product surface treating method of the Japanese Patent No. 3,049,230, there is used a treating liquid, which is an aqueous solution prepared by adding hydrogen peroxide into an aqueous acetic acid or formic acid solution and in which the concentration of the aqueous acetic acid or formic acid solution is in a range of 0.5 to 20 wt. % and the mole ratio of hydrogen peroxide/acid is in a range of 1.0 to 30, so as to epoxidize a part of double bonding portions of natural rubber or other diene based synthetic rubbers as represented in a chemical formula of FIG. 1, thereby enabling to provide a rubber product surface with non-adhesive property, sliding property and other barriering properties.
As a method for epoxidizing a double bond between carbons, it is known to adopt a peroxy acid of an organic compound, represented by a general formula of RCO3H. It includes performic acid, peracetic acid, perbenzoic acid and overphthalic acid. Simply immersing a rubber product in peroxy acid such as a peracetic acid aqueous solution (such as aqueous solution on the order of 1 to 4%) fails to provide a rubber product surface with a sufficient sliding property, and causes the rubber surface to be washed within the aqueous solution so that the adhesion property is rather strengthened. Further, trying an effective reaction at a peroxy acid concentration of 4% or more causes such a phenomenon of cracks on the rubber surface, thereby considerably deteriorating the physical properties of the rubber product.
As such, in the rubber product surface treating method of the Japanese Patent No.3,049,230, there is blended an excessive peroxide in a certain range of mole ratio to acetic acid or formic acid so as to cause the minimum organic acid to efficiently function, thereby allowing to epoxidize the surface layer of the rubber product to thereby provide it with non-adhesive property, sliding property and other barriering properties, without deteriorating the physical properties of the rubber product even in the presence of the peroxy acid of 1 to 4% or more.
In the rubber product surface treating method of the Japanese Patent No. 3,049,230, the epoxidation of the rubber surface is readily conducted. However, it is still desired to efficiently conduct a treatment in a shorter time, for practical use such as in factories.
The present applicant has thus found that the efficiency of epoxidation reaction can be improved in a shorter time by adopting a blended treating liquid of the present invention.